1. Field of the Invention
The present invention relates to a self-propelled building machine, in particular a road cutting machine or a surface miner, having a machine frame and a chassis that comprises running gear that rests on the ground below. Furthermore, the present invention relates to a method for operating such a building machine.
2. Description of the Prior Art
Self-propelled building machines of the above type comprise a working device that is arranged on the machine frame, which comprises a working roller that has to be brought into contact with the ground to work the ground below. This working roller can be in the form of a milling or a cutting roller, by means of which, for example, damaged layers of road can be removed, or mineral resources can be extracted from the ground.
In known road cutting machines and surface miners, the working roller is located in a roller housing which is open at the bottom, that is closed by a pressure element arranged in the direction of working in front of the working roller and by a stripper device arranged in the direction of working behind the roller. On at least one side, the roller housing is closed by a plate extending in the direction of working, which is designated as an edge protection.
The height of the machine frame of the known building machines can be adjusted in relation to the surface of the ground if the machine is positioned with the running gear resting on the ground. For this purpose, such building machines comprise a device for adjusting the height of the machine frame, which is activated by a control unit. As the working device is arranged on the machine frame, this adjustment affects not only the height of the machine frame, but also that of the working roller. In addition, the height of the working device can be adjusted in relation to the machine frame.
During the operation of the building machine, the height of the machine frame is set in such a way that the cutting roller of the working device penetrates the ground. At the same time, if necessary, the height of the pressure element and the stripper device and also of the edge protection can be adjusted in relation to the machine frame. In general, the pressure element, the stripper device and the edge protection are mounted in a floating manner, so that the height can be adjusted independently. This has the effect that the pressure element, the stripper device and the edge protection can follow the surface of the ground and the roller housing is always closed at the bottom.
When adjusting the working depth of the working device, the problem arises that, when the machine frame is lowered, the working roller does not penetrate the ground quickly enough. The speed at which the working roller penetrates the ground is determined by the condition of the working roller, the condition of the ground and the weight of the building machine. If the working roller does not penetrate the ground quickly enough and the machine frame is lowered further, there is a risk that the working roller will sink too deep into the ground. This problem is known in practice as a “sighting hole”.
It can also happen during the operation of the building machine that the edge protection, the stripper device or the pressure element, which are height-adjustably suspended or mounted on the machine frame, can become jammed while being adjusted. If the machine frame is lowered with the edge protection, the stripper device or the pressure element in a jammed state, it can happen that the building machine jerks backwards onto the running gears or the working roller if the jamming is suddenly released. This can damage the working roller or the drive train, for example.